Polymerization and polymerization catalysts



United States Patent --Earl W. Gluesenkamp and William R. Richard, Jr.,Dayton, Ohio, and John F. K. Wilshire, Kinghorn, Fife, Scotland,assignors to Monsanto Company, a corporation of Delaware No Drawing.Original application Mar. 3, 1958, Ser. No. 718,413. Divided and thisapplication Feb. 27, 1963, Ser. No. 290,269

6 Claims. (Cl. 260-943) This application is a division of the applicantscopending application Ser. No. 718,413, filed Mar. 3, 1958, now US.Patent No. 3,149,080.

The present invention is directed to use of polymerization catalysts inthe polymerization of olefinic materials.

The catalysts employed comprise in combination bis- (arene)metalcomplexes and metallo organic or metallic hydride reducing agents.

It has heretofore been known to polymerize ethylene in the presence ofcertain catalysts, commonly designated as Ziegler catalysts, in which aGroup IV to VI metal compound in which the metal is present in apositive valence state is admixed with certain reducing compounds asexemplified by trialkyl aluminum compounds or dialkyl aluminum hydrides.The presently disclosed catalysts differ radically from such Zieglercatalysts and involve an entirely different concept in that the metal inthe bis(arene)metal complex has an ionic valence of zero or may bequickly reduced to such zero valence state upon admixture with reducingagent, the saidmetal being held in the complex by a 1r-complex type ofbonding.

It is an object of the present invention to prepare and utilizecatalysts for the low-pressure polymerization of ethylene which aresoluble, at least in part, in common hydrocarbon solvents which areutilized as polymerization media. It is a further special object toemploy polymerization catalysts which are free from halides and similaranions which have a tendency to contaiminate polymeric products.

The bis(arene)metal complexes which are soluble in hydrocarbon solventsand constitute one of the components (or precursors) of the catalystemployed in the present invention can be represented by the followingsandwich structure, in which Tr represents a transition metal and inwhich benzene rings are exemplary of arene groups:

The transition metal is attached to the benzene rings by non-localizedcovalent bonds and is essentially in a zero valence state. Thebis(arene)metal complexes canv also be employed in the form of theirsalts, e.g. (C H Tr+Cl-, but the use of this form is undesirable,particularly in that it defeats one of the objects of the inventionwhich is to avoid the presence of halides or other contaminating anionsin the polymerization mixture. The bis(arene) metal complexes of any ofthe transition metals which form such complexes can be employed in thecatalysts of the present invention. As examples of such metals may bementioned iron, chromium, molybdenum, tungsten, etc.; the metals ofGroup VI-B, particularly those of atomic number up to 74, are preferred;and the metal Patented June 27, 1967 chromium is especially preferred.As the arene groups, almost any compounds containing aromaticunsaturation are suitable, so long as they do not contain substituentswhich interfere unduly. As examples of such groups may be mentionedbenzene, toluene, naphthalene, anthracene, mesitylene, diphenyl,tetralin, phenanthrene, ethylbenzene, butylbenzene, isobutylbenzene,sec-butylbenzene tbutylbenzene, hexylbenzene, etc. Other substitutedarene compounds are also suitable, particularly those which are stillessentially hydrocarbon in character, for example, fluorobenzene. It isgenerally convenient to utilize monocyclic arene compounds, i.e.,benzene. Those arene compounds containing no substituents other thanlower alkyl groups, for example, alkyl groups of up to 6 carbon atoms,are very suitable, particularly such monocyclic arene compounds. Asexamples of applicable bis(arene) metal complexes, the following'may bementioned: bis- (benzene)chromium, bis (toluene)chromium,bis(mesitylene)chromium, bis(tetralin)chromium, bis(diphenyl) chromium,bis(benzene)molybdenum, bis(diphenyl) molybdenum, bis(mesitylene)molybdenum, bis(benzene) tungsten, bis(mesitylene)tungsten,bis(benzene)iron, bis- (toluene)iron, bis(o-, m, p-xylene)iron,bis(mesitylene) .iron, bis(durene)iron, bis(hexamethylbenzene)iron, etc.

such complexes in the form of their salts with various anions. Thus, anyof the bis(arene)metal complexes given by way of example above can beemployed in the form of their salts, usually their monovalent salts, foradmixture with the reducing component to form the catalyst;

the salts can contain such anions, for example, as chloride, bromide,iodide, fluoride, etc.; anions of organic acids, such as acetate,propionate, benzoate, picrate etc.; anions of inorganic acids such assulfates, nitrate, phosphates, etc.; alkoxides, such as methoxide,ethoxide, isopropoxide, butoxide, etc.

The catalyst component having reducing properties can be defined ascomprising metals or metal compounds of the lst to 3rd groups of theperiodic chart of the elements.

A preferred group of such components are the organic compounds of metalshaving the general formula R M X in which R is hydrocarbon, M is a 1stto 3rd group metal, X is hydrogen or hydrocarbon, and n is a wholenumber which is lower by 1 than the valence of the metal M In theformula, X can also be halogen although it is desirable to avoid halogenfor reasons of product purity.

A particular group of organic compounds of metals which can be employedalong with the bis(arene)metal complexes are aluminum compounds of thegeneral formula RAlX where R is hydrogen or hydrocarbon, and X means anyother substituent including hydrogen or hydrocarbon; such compoundsinclude particularly dialkyl or diaryl aluminum monohalides, alsoaluminum hydride, alkyl or aryl aluminum dihydrides, dialkyl or diarylaluminum hydrides, alkyl or aryl aluminum dihalides, alkyl or arylaluminum dialkoxy or diaryloxy compounds. However, here, as above, itisv advantageous to avoid use of halogen. By way of example but notlimitation, the following such aluminum compounds are mentioned.

triethylaluminum triisobutylaluminum trioctylaluminumdidodecyloctylaluminum diisobutylaluminum hydride tridodecylaluminumdiphenylaluminum bromide dipropylcyclohexylaluminumditolylmethylaluminum tri-( fl-phenylethyl aluminum diethylaluminumchloride diisobutylaluminum chloride diisobutylaluminum iodide di,B-cyclohexylpropyl isobutylaluminum In one particular aspect, thepresent invention con cerns catalysts comprising bis(arene)metalcomplexes with trialkylaluminum compounds or dialkylaluminum hydrides.The use of these particular aluminum components, in addition to otheradvantages, avoids the presenceof halogens or similar materials whichwould contaminate the polymeric products.

Instead of or in addition to the organoaluminum compounds, organiccompounds of magnesium or zinc can be used, and these can contain eithera single or two hydrocarbon radicals, those of especial interest beingGrignard compounds, magnesium dialkyls, mixed organo zinc compounds suchas C H ZnI and zinc dialkyls, all of these, of course, being admixedwith bis(arene)metal complexes. It is also possible to employ thebis(arene)- metal complexes together With alkali metal alkyls, forexample, with lithium-, sodium-, or potassium methyl, -ethyl, -benzyl,-isobutyl, etc.

The present invention also contemplates catalysts useful in thepolymerization of ethylene which are formed by treating bis(arene)metalcomplexes with reducing agents such as: alkali metals, e.g., lithium,sodium, potassium; alkali hydrides, e.g., lithium hydride, sodiumhydride; complex alkali aluminum and alkali boron hydrides, e.g.,lithium aluminum hydride.

In general, the reducing components (or precursors) in the presentcatalysts can be any of the reducing ma terials which are used inpreparing the type of catalysts known as Ziegler catalysts.

It will be realized that reference herein to catalyst components asreducing components or as reducing agents does not require that suchcomponents act to reduce other catalyst componentsand, in fact, theyapparently form a complex with same-but rather indicates that a certainclass of known materials is contemplated.

Despite the broad scope of the reducing components utilizable incombination with the bis(arene) complexes of transition metals in thepresent catalysts, it will be found more convenient in most of thepresent application to discuss the invention with specific reference topreferred embodiments and, therefore, trialkylaluminum will be referredto especially by way of example. Likewise, bis(arene)chromium complexeswill be referred to especially by way of example of bis(arene)transition metal complexes.

The mole ratio or trialkylaluminum to bis(arene)metal complex, or statedanother and simpler way, the mole ratio of aluminum (Al) to transitionmetal (Tr), can vary over a wide range, suitable values being, forexample, 0.5:1 to 5:1 on up to :1 or higher. It is often preferred touse an AlzTr mole ratio of from about 1:1 to about 3:1. These ratios areapplicable, for example, to the Al/Cr ratio in general, and, by way ofspecific example, to the Al/Cr ratio in the catalyst, (isobutyl)' Al' (CH )Cr.

The present invention contemplates the polymerization of any monomers,the polymerization of which is catalyzed by heterogeneous metalcatalysts whichare capable of catalyzing the low-pressure polymerizationof ethylene; the ot-Ol6fiI1S are particularly suitable monomer-s forpolymerization.

At the present time, ethylene is the preferred monomer for use in thepolymerization of the present invention. The resulting polyethyleneordinarily has a molecular weight of at least 2000 and generally greaterthan 10,000. The present invention is particularly advantageous in thepreparation of polyethylenes of molecular weights ranging from 20,000 to50,000 or 100,000 and in many cases as high as 1,000,000 to 3,000,000 ormore. The molecular weights in question are those calculated in theconventional manner on the basis of the-viscosity of the polymer insolution as described in the Journal f'tir Practische Chemie, 2ndSeries, Vol. 158, page 136 (1941) and the Journal of the AmericanChemical Society, 73, page 1901 (1951). The ethylene can behomopolymerized or can be copolymerized with varying amounts,particularly on the order of 2 to 10 percent, of higher olefins such aspropylene, or butylene, especially the former. Other ethylenicallyunsaturated hydrocarbons can be polymerized by the agency of thecatalysts employed in the present invention, including propylene,butylenes, especially butene-l, amylenes and the like; substitutedolefins, such as vinylcyclohexane, styrene, vinylnaphthalene, vinylaromatic hydrocarbons generally, etc. In addition, a variety ofcopolymers of the various foregoing monomers named above with each otherand with other comonorners can be polymerized according to the presentinvention.

The amount of catalyst required is dependent on the other variablesof'the particular reaction, such as polymerization; and although amountsas small as 0.01 weight percent based on total weight of monomerscharged are sometimes permissible, it is usually desirable to usesomewhat larger amounts, such as from 0.1 up to 2 to 5 percent or evenconsiderably higher, say up to 20 percent, depending upon the monomer ormonomers, the presence or absence of solvent, the temperatures,pressures, and other reaction conditions. When polymerization iseffected in the presence of a solvent, the catalyst to solvent weightratio should be at least about 0.001z1 and much lower values suchas.0.0001:1 can sometimes be used.

The polymerization. can be effected over a wide range of temperatures,again the particular preferred temperature being chosen in accordancewith the monomer, pressure, particular catalyst and other reactionvariables. For many monomers from room temperature down to say 40 C. andeven lower are suitable, and in many cases, it is preferred that thetemperature be maintained at below about 35 C. However, for othermonomers, particularly ethylene,higher temperatures appear to beoptimum, say from 50 to 125 C. for ethylene, particularly to C.Temperatures ranging up to C. and higher are generally satisfactory forZiegler-type polymerization.

The pressure at which the polymerization is carried out is dependentupon the chosen monomer or monomers, as well as other variables. In mostinstances, the polymerization is suitably carried out at atmosphericpressure or higher. Subatmospheric pressures are permissible. Pressuresranging from atmospheric up to several hundred or even many thousandpounds per square inch, e.g., 50,000 p.s.i. and higher, are suitable,while high pressures are not required in order to obtain the reaction,they will have a desirable effect on reaction rate; and, in someinstances, on polymer quality. The choice of whether or not to use anappreciably elevated pressure will be one of economic and practicalconsiderations, taking into account the advantages that can be obtainedthereby.

The catalyst. is sensitive to various poisons, among which may bementioned oxygen, water, carbon dioxide, carbon monoxide, acetyleniccompounds such as acetylene, vinylaoetylene, alcohols, esters, ketones,aldehydes,

and the like. For this reason, suitable precautions should be taken toprotect the catalyst and the reaction mixture from excessive contactwith such materials. An excess of the aluminum compound tends to give acertain amount of protection against these poisons.

The catalyst, can be prepared in the vessel in which the catalyzedreaction is to be carried out, or it can be prepared in one vessel andthen transferred to the intended reaction vessel, and in either event,can either be used immediately after preparation or after a period oftime elapses between the preparation of the catalyst and its subsequentuse to catalyze, e.g., polymerization.

The catalyst can be prepared by simply adding the bis(arene)chromiumcomplex to the aluminum compound, or vice versa, preferably in thepresence of an inert organic solvent. Such solvents can suitably besaturated aliphatic and alicyclic, and aromatic hydrocarbons,halogenated hydrocarbons, and saturated ethers. The hydrocarbon solventsare generally preferred. By way of example can be mentioned liquefiedethane, propane, isbutane, normal butane, n-hexane, the various isomerichexanes, isooctane, cyclohexane, methylcyclopentane,dimethylcyclohexane, dodecane, industrial solvents composed of saturatedand/or aromatic hydrocarbons, such as kerosenes, naphthas, etc.,especially when hydrogenated to remove any olefin compounds and otherimpurities, and especially those ranging in boiling point up to 600 F.Also, benzene, toluene, ethylbenzene, cumene, decalin, ethylenedichloride, chlorobenzene, diethyl ether, o-dichlorobenzene, dibutylether, tetrahydrofuran, dioxane. In some instances, it is alsoadvantageous to prepare the catalyst in the presence of a monomer; forexample, if the catalyst is prepared in the presence of liquid ethyleneand then used to polymerize ethylene, a high yield of polyethyleneresults.

It may also be mentioned here that the polymerization can readily beeffected in the presence of any of the classes of solvents and specificsolvents just named. If the proportion of such solvent is kept low inthe reaction mixture, such as from to 0.5 part by weight inert organicsolvent (i.e., inert to the reactants and catalysts under the conditionsemployed) per 1 part by weight total polymer produced, solvent recoverysteps are obviated or minimized with consequent advantage. It is oftenhelpful in obtaining efiicient contact between monomers and catalyst andin aiding removal of heat of reaction, to employ larger amounts ofsolvent, for example, from 5 to 30 parts by weight solvent per 1 part byweight total polymer produced. These inert solvents, which are solventsfor the monomers, some of the catalyst components, and some of thepolymers, but are non-solvents for many of the polymers, e.g.,polyethylene, can also properly be termed inert liquid diluents or inertorganic liquids.

The polymer can be recovered from the reaction mixture by a wide varietyof procedures, chosen in accordance with the properties of theparticular monomer. It is usually desirable to remove as much catalystfrom it as possible-which is not especially difficult with the catalystsof the present invention, as removal of catalyst residues is easilyaccomplished with acid; the reaction mixture, or the polymer afterseparation therefrom, is contacted with hydrochloric acid solution; orcan be contacted with aliphatic alcohols, such as methanol, isobutanol,secondary butanol, etc. If the polymer is insoluble in the solvent, itcan be separated by filtration, etc.; if the polymer is soluble, it canbe precipitated by admixture of the solution with non-solvents, etc.

The following examples illustrate certain embodiments of the presentinvention.

Example 1 To a polymerization vessel containing 50 cc. kerosene, 0.64gram bis(benzene)chromium (3 millimoles) and 0.60 gram aluminumtriisobutyl (3 millimoles) were added. The vessel was then charged to1200 p.s.i. ethylene and heated and shaken at C. for 16 hours. Thepressure dropped to 400 p.s.i. during this time. The greenishwhitechunks of polyethylene obtained were stirred in a hydrochloricacid-acetone solution. The fine particles of polyethylene thus obtainedwere treated with 5% hydrochloric acid (containing a little acetone).The polyethylene was filtered from the liquid, washed three times withwater, twice with acetone, and once with pentane. The dried polyethyleneweighed 8.75 grams, for a production of 14 grams polyethylene/ grambis(benzene)chromium employed in the catalyst.

Example 2 A catalyst solution of 0.31 gram bis(benzene) chromium and0.30 gram aluminum triisobutyl in 50 cc. kerosene was prepared. Thecatalyst was then used to polymerize ethylene at 100 C. and an initialpressure of 600 p.s.i. The pressure had dropped to zero after 16 hours.The yellow solid polyethylene obtained was filtered from liquid andpulverized in a Waring Blendor in an acetonehydrochloric acid mixture.The resulting powder was boiled with acetone and 50% hydrochloric acidto give fluffy, white powder which was then washed successively withwater, acetone and pentane. The polyethylene powder, after being dried,weighed 9 grams, or 29 grams polymer/ gram of bis(benzene)chromiumemployed.

Example 3 In a polymerization vessel, 0.31 gram (1.48 millimoles) ofbis(benZene)Cr and 0.88 gram (4.4 millimoles) of Al(isobutyl) were mixedin 25 cc. of kerosene. Ethylene was then admitted (after the usualprecautions to remove air from the vessel) to a pressure of 720 p.s.i.,and the vessel was heated at 100 C. for 18 hours. Solid poly ethylenepolymer was obtained, which, after separation from the reaction mixture,weighed 3.3 grams. The amount of polyethylene produced Was 10 grams/grambis(benzene)chromium in the catalyst.

Pressures, such as from 100 p.s.i. to 2000 p.s.i. can conveniently beemployed in the present invention, but other pressures from atmosphericup to many thousands of pounds per square inch are also applicable.

The polyethylenes produced by the above procedures have densities offrom 0.9444 to 0.947 and are comparable to low-pressureZiegler-catalyzed polyethylenes in properties such as viscosity, tensilestrength and modulus of elasticity.

While the invention has been described with particular reference topreferred embodiments thereof, it will be appreciated that variationsfrom the details given herein can be effected without departing from theinvention in its broadest aspects.

What is claimed is:

1. In the polymerization of ethylene by contacting catalyst attemperatures from 50 to C. and pressures from atmospheric pressure to2000 p.s.i., the use of catalyst formed from bis(benzene)chromium and analuminum compound selected from the group consisting oftrialkylaluminums and dialkylaluminum hydrides.

2. The method of claim 1 in which the polymerization is conducted at atemperature of from 95 C. to 115 C. at pressure of from 100 to 2000pounds per square inch with an aluminum to chromium atomic ratio of from0.5 to 5.0.

3. The method of claim 1 in which aluminum triisobutyl is employed.

4. In the polymerization of a-olefins by contacting catalyst attemperatures from room temperature up to C. and pressures fromatmospheric pressure up to 2000 p.s.i., the use of catalyst formed froma bis(arene)metal 7 8 complex in which the metal is a Group VI-Btransition References Cited- JJEEZL if iffiZfiETiZE-l illii i 15 32325fii UNITED STATES PATENTS 1 11 Group mmetj p p 3,033,878 5/1962 Zeiss26094.9 3,051,690 8/1962 Vandenberg 26094.9

5. The method of claim 4 in Which the a-olefin is ethyl- 5 ene and thetemperature is from 50 to 125 C.

6. The method of claim 4 in which the metal complex JOSEPH SCHOFERPrmmry Examiner is bis(benzene)chromium. F. L. DENSON, AssistantExaminer.

1. IN THE POLYMERIZATION OF ETHYLENE BY CONTACTING CATALYST ATTEMPERATURES FROM 50* TO 125*C. AND PRESSURES FROM ATMOSPHERIC PRESSURETO 2000 P.S.I., THE USE OF CATALYST FORMED FROM BIS(BENZENE)CHROMIUM ANDAN ALUMINUM COMPOUND SELECTED FROM THE GROUP CONSISTING OFTRIALKYLALUMINUMS AND DIALKYLALUMINUM HYDRIDES.